Series editors' preface - Wood Tools

572 Conservation of Furniture
al., 1998). Immersion and vacuum impregnation
have been used in ceramics, paper and
paintings conservation but are generally
impractical for large pieces of furniture.
In all the methods described above the liquid
consolidant is introduced onto or into a surface
and converts in situ to a solid. It may be possible
to combine this approach with the use of
heat, for example if a liquid adhesive is introduced,
allowed to solidify and then treated with
a heated spatula. It is also possible to cast a thin
sheet of consolidant on Melinex/Mylar or silicon
release paper. A piece of cast consolidant
can be cut to the required shape and placed
under a flake. The consolidant can then be activated
with a small amount of solvent, a heated
spatula or both. The spatula should be hot
enough to soften or melt the consolidant without
damaging the decorative surface, and
should be isolated from the surface by
Melinex/Mylar. Heat sealing is suitable for Beva
371, or PVAC and acrylic adhesives with a Tg
lower than the temperature sensitivity of the
surface being consolidated. Heat sealing sometimes
has the advantage of softening flakes and
allowing them to be relaid flat.
Flakes, cups, tents and blisters
In the context of painted and decorative surfaces,
the term crack describes the fracture of
layer/s perpendicular to the plane of the surface.
Cracks may be caused by shrinkage of the
decorative layers as the binding medium dries.
Such cracks are not necessarily accompanied
by loss of adhesion or distortion from plane. In
some cases, cracks in a decorative surface may
lead to the formation of cups and flakes as a
result of internal stress, environmental conditions,
or a combination of both these factors.
Craquelure describes a fine network of shallow
cracks.
Strong cohesive properties within a particular
layer combined with weak adhesive properties
between layers will result in the formation
of flakes, cups, tents or blisters. These are vulnerable
to damage during handling, transport
or display and may result in loss if left
untreated.
The term cleavage describes loss of adhesion,
and may occur between paint or other
applied layers, between upper layers and
ground, or between ground and substrate. Loss
of adhesion can cause several types of charac-
teristic damage. Cups are usually small islands,
the edges of which have cleaved from the
lower layers or substrate and usually curl
upwards (out of plane distortion). Tents are
raised areas, cleaved from the lower layers or
substrate. The characteristic tent shape, in
which adjacent edges of the decorative surface
along a crack are forced upwards, is usually a
result of substrate shrinkage. Blisters combine
loss of adhesion with a bubble-shaped distortion
out of plane and are often a result of exposure
to heat. Blisters can be extremely difficult
to treat as there may be no way to introduce
consolidant without causing additional damage.
Flakes are a result of a total loss of adhesion,
resulting in loss of surface decoration.
If flaking, cupping or tenting is fresh it may
be possible to introduce consolidant underneath
and press it gently back into place. More
commonly, detached areas are brittle and
require additional treatment to allow them to be
laid without breaking them. Three options for
reducing the internal stress in a brittle detached
area are heat (alone or in combination with),
localized humidity or solvent. If the surface
cannot be rendered flexible by these treatments
it may be necessary to prevent loss by supporting
and adhering the detached area from
below using adhesive and an inert filler, e.g.
microballoons.
Moderate and localized heat, the temperature
dictated by the surface being treated, may be
applied with a heated spatula. Heat may be
applied to increase the penetration or working
time of a collagen or other heat sensitive/thermoplastic
adhesive or to soften a decorative
surface layer so that a detached area may be
flattened. Heat may also be applied after a thermoplastic
consolidant has set, for example the
following day. Humidity may be applied in a
variety of ways. A water-based consolidant
introduced under the flake, cup or tent may be
sufficient after a minute or two to soften it and
allow it to be laid flat. An ultrasonic pencil may
be used to introduce water vapour in a controlled
and localized manner. Moisture-sensitive
surfaces may be treated by indirect humidification,
e.g. a Gore-Tex sandwich (see section
15.2.2). The effect on the detached area should
be assessed regularly to check the effect on the
flake or cup and to ensure the surrounding area
is unaffected. Heat and localized humidity are
particularly effective in reducing the brittleness